JPH0366728B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium such as a magnetic tape, and more particularly to a magnetic recording medium having excellent dispersibility, solvent resistance, mechanical strength, etc. Conventionally, various types of resins have been synthesized that have double bonds in their molecules and can be cleaved by electron beam irradiation to form crosslinked network structures. Also,
A magnetic recording medium using a polyester resin having a hydrophilic sulfonic acid group in the molecule as a binder has good dispersibility, but has problems in that solvent resistance and mechanical strength are insufficient. Therefore, the present inventors have discovered that when used as a binder, for example, the good dispersibility of conventional polyester resins with sulfonic acid groups introduced therein can be further improved, while also having excellent mechanical strength and solvent resistance. We conducted intensive research on electron beam curable resins.
As a result, the electron beam cured polyester urethane acrylate has a sulfonic acid metal base that is more hydrophilic than a sulfonic acid base and has an excellent affinity with magnetic powder, and has double bonds at both ends of the molecule. It has been found that the polyester resin is also satisfactory in the above-mentioned respects. Furthermore, when the polyester-based urethane acrylate has one double bond at each end of the molecule, formation of crosslinks by electron beam irradiation is not necessarily sufficient; In polyester-based urethane acrylate having two or more functional groups, the formation of crosslinks is promoted, resulting in a stronger network structure after curing, which further improves mechanical strength and solvent resistance. This has led to the completion of the present invention. That is, the present invention provides a magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is provided on a nonmagnetic support, in which the binder has urethane bonds at both ends of the polyester molecule. It is an electron beam curable resin made of polyester urethane acrylate and has two or more double bonds at both ends of the molecule, and has a molecular weight of 1,000 to 50,000, and contains sulfone in the molecule. The present invention relates to a magnetic recording medium characterized in that it contains an electron beam curable resin containing a carboxylic acid component containing an acid metal base in an amount of 0.2 to 30 mol % based on the total carboxylic acid component. In the present invention, the polyester urethane acrylate contained in the binder is based on a copolyester resin having a sulfonic acid metal base in the molecule and having at least hydroxyl groups at both ends. It can be obtained by reacting a polyester urethane obtained by reacting a trifunctional or higher functional polyisocyanate compound with an acrylic or methacrylic monomer having a hydroxyl group and a double bond at the end of the molecule. The carboxylic acid component of the copolymerized polyester resin used in the present invention includes terephthalic acid,
Aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, 1,5-naphthalic acid, dicarboxylic acids such as aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecane dicarboxylic acid, p-oxybenzoic acid , aromatic oxycarboxylic acids such as p-(2-hydroxyethoxy)benzoic acid, tricarboxylic acids such as trimellitic acid, trimesic acid, pyromellitic acid, and tetracarboxylic acids. Particularly preferred carboxylic acids include terephthalic acid, isophthalic acid, adipic acid, and sebacic acid. The polyhydric alcohol component which is another component of the copolymerized polyester resin used in the present invention includes ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, Neopentyl glycol, 1,6-hexanediol,
Aliphatic diols such as 2,2,4-trimethyl-1,3-pentanediol or substituted derivatives thereof, cycloaliphatic diols such as 1,4-cyclohexanedimethanol, diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, Diols such as polyalkylene glycols such as polytetramethylene glycol, aromatic diols such as ethylene oxide adducts or propylene oxide adducts of bisphenol A, ethylene oxide adducts or propylene oxide adducts of hydrogenated bisphenol A Examples include oxides such as alkylene oxide adducts. Furthermore,
Polyhydric alcohols such as triols or tetraols such as trimethylolethane, trimethylolpropane, glycerin, pentaerythritol can also be used, but these polyhydric alcohols are preferably used in combination with diols. Examples of the polycarboxylic acid having a sulfonic acid metal group, which is another component of the copolymerized polyester resin used in the present invention, include 2-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid, 5-sodium sulfoisophthalic acid, Preferred examples include aromatic dicarboxylic acids containing an alkali metal sulfonate base such as 5-potassium sulfoisophthalic acid; however, organic acids listed as the carboxylic acid component mentioned above and having a metal base sulfonate are preferred. You can use any of them. As the sulfonic acid metal base, it is preferable to use an alkali metal base. The content of the carboxylic acid component containing these sulfonic acid metal bases is preferably about 0.2 mol% to 30 mol%, and about 0.5 mol% to 10 mol%, based on the total carboxylic acid components. is preferable. If the carboxylic acid component having such a sulfonic acid metal base is too small, an electron beam curable resin with excellent dispersibility cannot be obtained, and if the carboxylic acid component is too large, the solubility in general-purpose solvents will be poor. Good paint cannot be obtained. In the present invention, as described above, at least the hydroxyl groups at both ends of the copolymerized polyester resin as described above are reacted with a trifunctional or higher functional polyisocyanate compound, and at least two
It is possible to obtain a polyester-based urethane having four or more functional groups having four or more isocyanate groups. 3
As polyisocyanate compounds with more than functional functions,
Trifunctional or higher functional polyols (e.g. glycerin,
A reaction product of trimethylolpropane, pentaerythritol, dipentaerythritol) and a bifunctional isocyanate compound (for example, tolylene diisocyanate, hexamethylene diisocyanate, diphenylmethane diisocyanate) can be used. Commercially available trifunctional isocyanate compounds include T-100 (manufactured by Toray Industries, Inc.), Takenate D110N (manufactured by Takeda Pharmaceutical Co., Ltd.), Coronate L (manufactured by Nippon Polyurethane Industries, Ltd.), and Desmodyur N (manufactured by Bayer Pharmaceutical Co., Ltd.). Tetrafunctional isocyanate compounds include Desmodyur IL and Desmodyur CT (both manufactured by Bayer). The compound used to introduce two or more double bonds into at least both ends of the polyester urethane mentioned above is an acrylic compound having a hydroxyl group and a double bond at the end of the molecule; Methacrylic monomers may be used. Such monomers have the general formula:

[Formula] (In the formula, R ₁ means a hydrogen atom or a methyl group,
And R ₂ means an unsubstituted or substituted alkylene group. ) is used. In the above general formula, the alkylene group is a linear or branched divalent saturated hydrocarbon residue having 1 to 12 carbon atoms. This alkylene group also includes a halogen atom, an alkyloxy group having 1 to 4 carbon atoms which may be substituted with 1 to 3 halogen atoms, and an alkyloxy group having 2 to 4 carbon atoms which may be substituted with 1 to 3 halogen atoms.
alkenyloxy group having 2 to 4 carbon atoms;
may be substituted with a substituent such as an alkenylcarbonyloxy group. Preferred examples of the compounds represented by the above general formula include 2-hydroxyethyl ester, 2-hydroxypropyl ester, 2-hydroxybutyl ester, 2-hydroxyoctyl ester, and 2-hydroxypropyl ester of acrylic acid or methacrylic acid.
-Hydroxydodecyl ester, 2-hydroxy-3-chloropropyl ester, 2-hydroxy-3-acryloxypropyl ester, 2-hydroxy-3-methacryloxypropyl ester, 2-hydroxy-3-acetoxypropyl ester, 2-hydroxy -3-chloroacetoxypropyl ester, 2-hydroxy-3-dichloroacetoxypropyl ester, 2-hydroxy-3-trichloroacetoxypropyl ester,
Examples include 2-hydroxy-3-crotonyloxypropyl ester and 2-hydroxy-3-allyloxy ester. In addition to these preferred compounds, any monomer having an active hydrogen that reacts with the isocyanate group of the polyester urethane and an acrylic or methacrylic double bond can be applied to the present invention. In the present invention, the polyester urethane acrylate having the above-mentioned structure has a molecular weight of about 1,000 to about 50,000. If the molecular weight is smaller than 1,000, it is difficult to synthesize, and if the molecular weight is larger than 50,000, the molecular weight between crosslinking points increases, which tends to reduce the Young's modulus of the coating film, which is undesirable. Unfavorable for dispersing magnetic powder. The electron beam curable resin used in the present invention can be produced by a conventional method. For example, a copolymerized polyester resin is first prepared in a conventional manner using the above-mentioned carboxylic acid, a carboxylic acid containing a sulfonic acid metal base, and a polyhydric alcohol so as to have an appropriate molecular weight, and then a copolymerized polyester resin is prepared using a conventional method. A tetrafunctional or higher-functional polyester system having at least two or more isocyanate groups at each end of the molecule, obtained by reacting a polyisocyanate compound and bonding at least the hydroxyl groups at both ends of the copolymerized polyester resin with the isocyanate groups. After synthesizing the urethane, two acrylic or methacrylic double bonds are formed at both ends by reacting the isocyanate groups of the polyester urethane with the acrylic or methacrylic monomers described above. It is possible to produce a polyester-based urethane acrylate having four or more functional groups. In the magnetic recording medium according to the present invention, the electron beam curable resin made of polyester urethane acrylate produced as described above is used alone or mixed with other resins as a binder, but during the total bonding, It is preferable that the content is at least % by weight. This is because if it is less than 20% by weight, it becomes difficult to form a crosslinked structure, and the effects of solvent resistance, mechanical strength, and dispersibility due to the metal sulfonate base cannot be expected. In the magnetic recording medium according to the present invention, other resins that can be mixed with the electron beam curable resin and used as a binder include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, Vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer,
Acrylic acid ester-vinylidene chloride copolymer,
Methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer,
Thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral , cellulose derivatives, styrene-butadiene copolymers, polyester resins, phenolic resins, epoxy resins, thermosetting polyurethane resins, urea resins,
Examples include melamine resins, alkyd resins, urea-formaldehyde resins, and mixtures thereof. In the present invention, the magnetic powder constituting the magnetic layer includes γ-Fe ₂ O, Fe ₃ O ₄ , iron oxide in an oxidation state intermediate between γ-Fe ₂ O ₃ and Fe ₃ O ₄ , Co-containing γ-Fe _{2 O3} , Co
Iron oxide in an oxidation state intermediate between γ-Fe ₂ O ₃ and Fe ₃ O ₄ , iron oxide containing one or more metal elements (especially transition metal elements), iron oxide containing Co oxide CrO 2 , those with a coating layer mainly composed of hydroxides, oxide-based magnetic powders such as CrO ₂ , those with a Cr ₂ O ₃ layer formed by reducing the surface of CrO ₂ , or Fe, Co, Ni, etc. metal or Fe-Co
Alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Co-Ni
-P alloy, Co-Ni-Fe-B alloy, Fe-Ni-Zn
Ferromagnetic fine powders such as alloys, Fe-Mn-Zn alloys, Fe-Co-Ni-P alloys, etc. can be used. The magnetic layer also contains reinforcing agents such as aluminum oxide, chromium oxide, and silicon oxide.
Carbon black or the like may be added as an antistatic agent, and molybdenum disulfide, graphite, silicone oil, olive oil, or the like may be added as a lubricant. The constituent materials of the magnetic layer as described above are generally dissolved in a solvent to prepare a magnetic paint. The solvent includes ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohols such as methanol; methyl acetate,
Esters such as ethyl acetate, butyl acetate, and ethyl butyrate; Glycol ethers such as ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, and dioxane; Aromatic hydrocarbons such as benzene, toluene, and xylene; Hexane,
Aliphatic hydrocarbons such as heptane or mixtures thereof can be used. Furthermore, the above-mentioned magnetic paint is applied onto a non-magnetic support. Materials for the nonmagnetic support that can be used include, for example, polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polycarbonate, polyvinyl chloride, polyimide, metals such as aluminum and copper, Examples include non-magnetic materials such as paper. It is desirable to apply a magnetic paint having the above-mentioned structure onto a non-magnetic support by a conventional method and dry it, then calender the coating film and then irradiate it with an electron beam. You can also. As the electron beam to be irradiated, in addition to electron beams, ionizing radiation such as neutron beams and gamma rays can be used, and electron beams are preferable from an industrial perspective. The irradiation radiation is preferably about 1 to 10 Mrad, more preferably about 2 to 7 Mrad. When using an electron beam accelerator for irradiation, the irradiation energy (acceleration voltage) is preferably about 100 KeV or more. The present invention will be explained below using examples. In addition,
All units (parts) used in Examples and Comparative Examples are parts by weight. Example 1 Synthesis of polyester urethane acrylate Dimethyl terephthalate 119.2 was added to a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser.
parts, dimethyl isophthalate 89.4 parts, 5-sodium sulfoisophthalate 136.5 parts, ethylene glycol 148.2 parts, neopentyl glycol
203.4 parts, and 0.025 zinc acetate as catalyst
180 parts and 0.003 parts of sodium acetate.
The transesterification reaction was carried out at 220°C for 3 hours. Then, 376.2 parts of sebacic acid was added,
After reacting at 200°C to 240°C for 2 hours, the reaction system was depressurized to 10 mmHg over 30 minutes. This reaction system was further subjected to a polycondensation reaction at a temperature of 250° C. for 2 hours under a pressure of 3 to 10 mmHg. The copolymerized polyester resin thus obtained has a reduced viscosity η _SP/c = 0.156 (methyl ethyl ketone:toluene = 1:1, 30°C) and a hydroxyl value of 42
It was hot. As a result of analyzing this copolymerized polyester resin by nuclear magnetic resonance (NMR) analysis, etc., its composition was as follows. Terephthalic acid 20 mol%, isophthalic acid 15 mol%, sodium 5-sulfoisophthalate 5 mol%, sebacic acid 60 mol%, ethylene glycol
50 mol% and neopentyl glycol 50 mol%. Next, 50 parts of the copolyester resin obtained above and 73 parts of methyl ethyl ketone were added to a reaction vessel equipped with a thermometer, a stirrer, and a reflux condenser.
1 part, 73 parts of toluene, 17 parts of Coronate L (manufactured by Nippon Polyurethane Kogyo Co., Ltd.) and 0.005 part of dibutyltin dilaurate were charged, and the mixture was reacted at 70°C to 90°C for 3 hours. The NCO group concentration of the polyester urethane thus obtained was 780 mmol/g.
It was hot. Furthermore, this polyester urethane has β
- When 19.1 parts of hydroxyethyl methacrylate was added and reacted at 70°C to 90°C for 3 hours,
Reduced viscosity η _SPC /C = 0.182 (methyl ethyl ketone: toluene = 1:1, 30°C), number average molecular weight
3900 tetrafunctional polyester urethane acrylate was obtained. 2. Preparation of Magnetic Tape A mixture of 10 parts of γ-Fe ₂ O ₃ magnetic particles, 5 parts of methyl ethyl ketone, and 7.5 parts of toluene was kneaded for 3 hours using a ball mill. Add to this mixture 2.5 parts of polyester urethane acrylate produced as described above and 5 parts of methyl ethyl ketone.
A mixed solution of 1 part and 7.5 parts of toluene was added and kneaded again for 24 hours using a ball mill. After degassing the resulting mixture, it was coated onto a 16μ thick polyethylene terephthalate film using a doctor blade with a 25μ gap to a dry thickness of 8.0μ, and then placed in a parallel magnetic field of 900Oe for approximately 1 It was left still for a second. Next, the material was left in a hot air dryer at 90.degree. C. for about 30 minutes to remove the solvent, and then supercalendered. Furthermore, the magnetic layer of this tape was irradiated with 5 Mrad of electron beams at an accelerating voltage of 200 KV to harden the magnetic layer, and then cut into 1/2 inch width to obtain the desired magnetic tape. Comparative Example 1 50 parts of the copolyester resin obtained in the example, 70 parts of diphenylmethane diisocyanate, and 0.005 parts of dibutyltin dilaurate were charged into a reaction vessel equipped with a temperature system, a stirrer, and a reflux condenser, and the mixture was heated at 70°C to The reaction was carried out at 90°C for 3 hours. NCO of polyester urethane obtained in this way
The group concentration was 390 mmol/g, and the reduced viscosity η _SP/C =0.193 (methyl ethyl ketone:toluene = 1:1, 30°C). Next, 9.54 parts of β-hydroxyethyl methacrylate was added to this polyester urethane.
When the reaction was carried out at 70°C to 90°C for 3 hours, the reduced viscosity η _SP/C = 0.163 (methyl ethyl ketone: toluene =
A difunctional polyester-based urethane acrylate having a number average molecular weight of 4,380 was obtained. Using the thus obtained bifunctional polyester urethane, a magnetic tape was produced in the same manner as in the example. Comparative Example 2 In the copolymerized polyester resin of Example, 5
- Using isophthalic acid instead of sodium sulfoisophthalic acid, a tetrafunctional polyester-based urethane acrylate containing no sulfonic acid metal base was synthesized in the same manner as in the example. A magnetic tape was produced in the same manner as in the example using the thus obtained polyester urethane acrylate containing no sulfonic acid metal base. The tensile strength of the polyester urethane acrylates obtained in Examples and Comparative Examples 1 and 2 was measured. The polyester urethane acrylates of Examples and Comparative Examples 1 and 2 were each dried at 90℃ and 25mmHg for 3 days to form a film of about 100μ, and then heated to 200KV.
A cured film was obtained by irradiating an electron beam at an acceleration voltage of 5 Mrad. From this cured film, a tanzak mold with a width of 0.625 cm and a length of 10 cm was cut out and measured using a universal tension tester. The results are shown in Table 1.

[Table] As is clear from Table 1, the polyester urethane acrylates of Examples and Comparative Example 2 were
Compared to Comparative Example 1, both breaking strength and Young's modulus are significantly superior. The polyester urethane acrylates of Examples and Comparative Example 2 have four double bonds in one molecule, whereas Comparative Example 1 has two double bonds. This indicates that the more polyfunctional polyester urethane acrylate is, the more effectively crosslinking occurs when irradiated with an electron beam, and the strength is improved. Next, various properties of the magnetic tapes obtained in Examples and Comparative Examples 1 and 2 were measured. 1 Squareness ratio Rs (Br/Bm) 2 Tensile strength The above-mentioned hardened examples and comparative examples 1 and 2
A 0.625 cm wide and 10 cm long strip was cut out from the magnetic tape and measured using a universal tension tester. 3 Solvent resistance The magnetic layer was rubbed with gauze containing methyl ethyl ketone, and the number of times the layer was rubbed until the layer disappeared was expressed as the number of times the layer was rubbed. 4. Powder falling off When the tape was actually run, the amount of powder adhering to the pinch roller, capstan, guide head, etc. was expressed on a scale of 0 to -5 using a subtraction system. Test results for each tape are shown in Table 2.

[Table] From the above results, in Example and Comparative Example 1, Rs.
Although there is no difference in Young's modulus, solvent resistance, and powder shedding, it can be seen that the Example is significantly improved compared to Comparative Example 1. This is because the polyester-based urethane acrylate used as the binder in the magnetic tape of the example was tetrafunctional, and Comparative Example 1 using a di-functional polyester-based urethane acrylate.
This is because crosslinking in the magnetic layer was significantly promoted compared to the case of . In addition, in Examples and Comparative Example 1 using polyester urethane acrylate containing a metal sulfonate base, Rs is smaller than in Comparative Example 2 which does not contain a metal base sulfonate.
From this, the effect of the sulfonic acid metal base on the dispersibility is clear.

Claims (1)

[Claims] 1. In a magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is provided on a non-magnetic support,
The binder is an electron beam curable resin made of polyester urethane acrylate, in which urethane bonds exist at both ends of the polyester molecule, and two or more double bonds exist at each end of the molecule. and its molecular weight is 1000 to 50000
A magnetic recording medium characterized in that it contains an electron beam curable resin in which the molecule thereof contains a carboxylic acid component containing a sulfonic acid metal base in an amount of 0.2 to 30 mol% based on the total carboxylic acid component. .